“Necessity may be defined in two ways, conformably to the two definitions of cause, of which it makes an essential part. It consists either in the constant conjunction of like objects, or in the inference of the understating from one object to another.”
§ 8.27
An Enquiry Concerning Human Understanding (1748)
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David Hume 138
Scottish philosopher, economist, and historian 1711–1776Related quotes

Lecture XX, "Conclusions"
1900s, The Varieties of Religious Experience (1902)

in p. 125.
Sources, The Yoga Darsana Of Patanjali With The Sankhya Pravacana Commentary Of Vyasa

Source: Argumentation and debating, 1908, p. 27; partly cited in: Branham (2013, p. 39)

“Every definition implies an axiom, since it asserts the existence of the object defined.”
Part II. Ch. 2 : Mathematical Definitions and Education, p. 131
Science and Method (1908)
Context: Every definition implies an axiom, since it asserts the existence of the object defined. The definition then will not be justified, from the purely logical point of view, until we have proved that it involves no contradiction either in its terms or with the truths previously admitted.
[The Tangled Bank: Darwin, Marx, Frazer and Freud as Imaginative Writers, New York, Atheneum, 1962, ; 492 p.] [2nd edition, 1974, https://books.google.com/books?id=Fm8fAAAAMAAJ&focus=searchwithinvolume&q=conflict] (p. 312)

A Neglected Argument for the Reality of God (1908)
Context: Of the three Universes of Experience familiar to us all, the first comprises all mere Ideas, those airy nothings to which the mind of poet, pure mathematician, or another might give local habitation and a name within that mind. Their very airy-nothingness, the fact that their Being consists in mere capability of getting thought, not in anybody's Actually thinking them, saves their Reality. The second Universe is that of the Brute Actuality of things and facts. I am confident that their Being consists in reactions against Brute forces, notwithstanding objections redoubtable until they are closely and fairly examined. The third Universe comprises everything whose being consists in active power to establish connections between different objects, especially between objects in different Universes. Such is everything which is essentially a Sign — not the mere body of the Sign, which is not essentially such, but, so to speak, the Sign's Soul, which has its Being in its power of serving as intermediary between its Object and a Mind.
[Poverty in the United Kingdom: A Survey of Household Resources and Standards of Living, 1979, University of California Press, 978-0-520-03976-6, 31, https://books.google.com/books?id=weGYy_-czvsC&pg=PA31]